[wip] Add allowDuplicateFiles option to @uppy/core

[arturi]

Allow duplicate files to be added to Uppy (optionally). If the fileId exists, we either throw an error, or generate a new unique file id, so that a copy of the file can be added:

Fixes #843 #1179 #754

Does this break something for Golden Retriever and Tus?

todo:

• tests
• docs
• figure out the default, and whether we want to add an “overwrite” option — current behavior

[goto-bus-stop]

tus resume: true would interfere with this at the moment, because it has its own fingerprint generation. it might be ok if we override the fingerprint option and use the Uppy-generated file ID… i think golden retriever may be fine because it already uses the IDs provided by uppy.

this feature does add an entire new axis to think about in every other patch though :D i don't think a native file input supports this and i'm not really sure of the use case?
e; seems like the linked issues are mostly talking about adding the same file after a previous upload, that does make sense.

[arturi]

Closed, because this feature might break some other features, like tus resumability, and requires more thinking through, and we didn’t want unexpected breakage before 1.0 release.

[jvelten]

Will an option to allowDuplicateFiles released?
We have some use-cases for supervisors they need to upload the same file (path, name, source is equal) into the mediacenter of different users.